We can't say for sure what happened but the behaviors afterwards and what evidence does exist points to the event not having occurred, so most rational people will come to the conclusion that the event, as described, was fabricated.
What "evidence that does exist"?
No, seriously. What evidence? It's literally "Sulkowicz's behavior", which, for the millionth time, is entirely based on subjective interpretation, AKA "feels". Again, that exact same behavior could be interpreted by someone just as rational as you to SUPPORT Sulkowicz's story. Again, based on "feels".
People treat "feels" like it's a bad word. It's not. We all make feels-based deductions every day. We base our deductions on our personal experiences and things we have observed in our years on this planet. The problem lies in trying to pass off our "feels" as fact. No, Brikker, you do not have the authority to claim what conclusion "most rational people" will come to. That's a foolish statement literally based on nothing but more "feels". "I came to this conclusion and I believe I am rational, therefore I assume most rational people will come to the same conclusion." ...See the problem there?
If this were any other discussion, the claim that "most rational people" believe Sulkowicz was lying would be met with "based on what?" and demands for both stats on how many people believe that and proof that they are, in fact, rational. In fact, even if such stats were available they would be correctly called out as an "appeal to popularity" fallacy. However, because it's a narrative that's very popular on this message board, we have forgone basing these conclusions on facts and, as a group, decided that feels can substitute for facts in this situation. It's silly.
There is no proof Sulkowicz was lying. There is no proof she was telling the truth. You can personally believe whatever you like, but when it comes to what can be PROVEN, the only possible conclusion is "We don't know what happened".